3.5 Process Water Treatment

Calders and Grandidge Limited - process water treatment plant

The process flow diagram illustrates a water treatment plant used for the removal of creosote and pesticides from the liquid phase in a timber treatment facility. A storage tank is used for smoothing the flow, from where the water is pumped into a chemical dosing system for pH adjustment. At this stage, ferric sulphate is added to form a precipitate with suspended solids, which is subsequently flocculated by the addition of polyelectrolyte.

Water is then pumped through series operated sand filters, which provide the final stage of suspended solids removal and protect the granular activated carbon (GAC) filters from particulate contamination. Series operated GAC filters are then used to remove the dissolved creosote and pesticides from the water. To ensure compliance with specification levels, the water is sampled and analysed after the first GAC filter. The second GAC filter acts as a guard bed.

Process water treatment plant at Calders and Grandidge Ltd

The unique feature of this adsorption system is the use of dual GAC media beds. By careful selection of the GAC it was possible to install two types of GAC, which function as discrete layers. The top portion of the adsorber was filled with Filtracarb CC60/1240, which acts as a sacrificial layer, removing bulky organic compounds. Filtracarb SX5 was installed under this layer, providing a highly retentive media for maximum adsorption efficiency.

CPL Carbon Link manufactures a range of coal and coconut shell GAC products for process water treatment. The key features of these products are;

• Range of activity levels and pore size distributions provide a flexible approach to adsorption
• Excellent product hardness to resist mechanical attrition
• A wide range of particle sizes
• Spent material can be thermally reactivated